Typically, a solid oxide fuel cell (SOFC) employs an electrolyte of ion-conductive solid oxide such as stabilized zirconia. The electrolyte is interposed between an anode and a cathode to form an electrolyte electrode assembly (MEA). The electrolyte electrode assembly is interposed between separators (bipolar plates). In use, generally, predetermined numbers of the electrolyte electrode assemblies and the separators are stacked together to form a fuel cell stack.
In the fuel cell, in order to supply a fuel gas such as a hydrogen-containing gas and an oxygen-containing gas such as air to the anode and the cathode of the electrolyte electrode assembly, respectively, a fuel gas channel and an oxygen-containing gas channel are formed along surfaces of the separator.
For example, in a solid oxide fuel cell disclosed in Japanese Laid-Open Patent Publication No. 05-129033, as shown in FIG. 33, unit cells 1a and separators 2a are stacked alternately to form a fuel cell stack 3a. A plurality of air supply holes 4a and fuel supply holes 5a are formed alternately at one end of the separators 2a, and a plurality of air discharge holes 6a and fuel discharge holes 7a are formed alternately at the other end of the separators 2a. In the fuel cell stack 3a, the fuel and the air flow in parallel to each other in the same direction on both of front and back surfaces of the unit cells 1a. 
In a flat plate type solid oxide fuel cell disclosed in Japanese Laid-Open Patent Publication No. 10-172594, as shown in FIG. 34, unit cells 1a and separators 1b are provided alternately, gas supply holes 2b and gas discharge holes 3b extend through four corners of the separator 1b in the stacking direction, and a plurality of gas flow grooves 4b are formed on both surfaces of each separator 1b. 
The gas from the gas supply hole 2b flows through a triangular recess 5b, and flows into the gas flow grooves 4b. A gas inlet is formed in an area close to the gas supply hole 2b of the triangular recess 5b. In the gas inlet, at least one of a throttle section 6b and blocks 7b is provided. The throttle section 6b and the blocks 7b function to increase the pressure loss in the gas flowing from the gas supply hole 2b. 
In the stack structure adopted in a flat type solid oxide fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2007-026925, as shown in FIG. 35, a plurality of flat type unit cells 1c and separators 2c are stacked together alternately. The separator 2c is formed by stacking a center plate 3c, a fuel electrode plate 4c, and an air electrode plate 5c. 
A fuel gas supply flow field 6c is formed on a surface of the center plate 3c, and a plurality of fuel gas injection through holes 7c are formed in the fuel electrode plate 4c. The fuel gas injection through holes 7c are connected to the fuel gas supply flow field 6c. An oxygen-containing gas supply flow field 8c is formed on the back surface of the center plate 3c. A plurality of oxygen-containing gas injection through holes 9c are provided in the air electrode plate 5c. The oxygen-containing gas injection through holes 9c are connected to the oxygen-containing gas supply flow field 8c. 